1. Field of the Invention
This invention relates to systems for anchoring tissue to bone, and more specifically, to a system for testing the strength of sutures and anchors.
2. Background Information
Systems and devices for anchoring sutures to bone are commonly used in medical or surgical operations. Anchored sutures are typically used to attach soft tissue, such as is ligaments, tendons and muscles, to bone or to attach inanimate objects, such as prostheses, to bone. The attachment may be intended to hold the tissue to a bone long enough for healing to occur or for a more extended period of time (e.g., for the life of the patient). Alternatively, the attachment may be intended to hold tissue in place temporarily (e.g., only during the surgical procedure).
Conventional suture anchors are typically inserted into a bore or hole that has been previously drilled into the bone. Alternatively, they can be driven directly (e.g., hammered or screwed) into the bone in which no previous bore or hole has been made. Most bone anchors include some type of mechanism, such as ridges, threads, spikes, barbs, etc., that extend from the anchor and are intended to firmly attach the anchor to the bone. Many operations require the installation of multiple anchors in the patient""s bone. Once the anchor has been secured to the bone, the suture(s) can then be attached, typically by knots, to the anchor. Alternatively, the sutures may be pre-attached to the anchor before it is installed into the bone.
Installation tools, specifically designed to install bone anchors, are also known. These tools typically assist the surgeon in inserting the anchors into the pre-formed bores or holes or in driving the anchors into the bone.
Depending on the tissue being secured, the load imposed on sutures and the corresponding anchors can vary significantly. The load on sutures and anchors can also vary depending on the patient. For example, for a given procedure, the loads imposed on sutures and anchors by a professional athlete may be significantly greater than the loads imposed by others and far less than might be imposed by the elderly. The loads imposed on the sutures and anchors may result in failures. That is, the anchors can be pulled from the bone or the sutures may break. Since anchors are relatively small and can be installed in arthroscopic surgeries, it can be difficult for surgeons to evaluate how well the installation has been done. In addition, unknown to the surgeon, the anchors can be installed in weakened bone mass precipitating a failure. Furthermore, the sutures may be xe2x80x9cknickedxe2x80x9d or otherwise damaged during installation compromising their strength.
Briefly, the invention is directed to a system for ensuring that sutures and anchors satisfy some minimum strength threshold in vivo (e.g., during the respective operation or procedure). The invention includes a handle that contains a sensor or transducer for measuring forces or loads (e.g., a strain gauge), an indicator, and a controller. The controller is arranged in communicating relationship with the sensor and the indicator. During use, a surgeon installs an anchor into a patient""s bone. To test the strength of the anchor, the sensor is connected to the anchor preferably by some mechanical linkage, such as a rod or shaft. The surgeon then pulls on the handle. By pulling on the handle, a corresponding force is applied to the anchor through the mechanical linkage, which may extend from the handle. As the surgeon pulls, the controller receives a signal from the sensor that is proportional to the force or load being applied to the anchor. In the illustrative embodiment, the controller is configured to compare the sensor signal to some predetermined threshold. When the signal exceeds the threshold, the controller activates the indicator (which may be a visual or audio indicator), thereby alerting the surgeon that the anchor has withstood the requisite load or force, and is thus securely attached to the patient""s bone.
The surgeon may also, or in the alternative, test the strength of the sutures and the anchor together. In this case, the surgeon connects one or more sutures to the anchor, unless the sutures were pre-attached to the anchor. The sutures are then connected to the sensor either directly or through some linkage. Again, the surgeon pulls on the housing of the system, thereby applying a corresponding force to the sutures. When the force or load applied to the sutures exceeds the pre-determined threshold, the controller activates the indicator.
In another embodiment of the invention, the handle may further contain an input device that is also in communicating relationship with the controller. By manipulating the input device, the surgeon can adjust the threshold utilized by the controller. In this embodiment, the controller activates the indicator when the sensor signal exceeds the threshold as set by the input device. In this way, the surgeon can select the particular force or load that the anchor or sutures must satisfy during the operation or procedure.
In yet another embodiment, the system includes a drive mechanism that allows the surgeon to test the strength of the anchor or sutures without having to pull on the handle. The drive mechanism includes a support that extends from the handle and engages the patient. The drive mechanism further includes an actuator that moves the sensor away from the patient. In use, the anchor or sutures are connected to the sensor. The actuator is then started, pulling the sensor away from the patient, thereby imposing a force or load onto the anchor or sutures. When the signal from the sensor exceeds the threshold, indicating that the force or load on the anchor or sutures exceeds the minimum level, the controller activates the indicator.